A battery is a device that converts the chemical energy contained in its active materials directly into electrical energy by means of an electrochemical oxidation-reduction reaction. This type of reaction involves the transfer of electrons from one material to another through an electric circuit when the battery is placed under a load. A battery typically comprises one or more electrochemical cells connected in series, parallel, or both, depending on desired output voltage and capacity. Each cell principally comprises an anode, a cathode, and an electrolyte. The anode, or negative electrode, gives up electrons to the external circuit and is oxidized during the electrochemical reaction. The cathode, or positive electrode, accepts electrons from the external circuit and is reduced during the electrochemical reaction. The electrolyte serves as the ionic conductor and provides the medium for transfer of ions inside the cell between the anode and the cathode, and typically comprises liquid, solid or gel materials. Some batteries are intended for single use, and once discharged are discarded (commonly termed as primary batteries). Other batteries are more readily designed to be recharged essentially to their original condition upon discharge (commonly termed as secondary batteries).
Periodic table Group 1A and Group 2A metals, and particularly lithium, are attractive as battery anode materials because of their light weight, high voltage, high electrochemical equivalence, and good conductivity. One type of battery comprises a reactive metal-water battery, such as a Li-water battery. Such batteries today are principally fabricated for low power and long duration, but may find other uses. With such a battery, the reactive metals such as lithium serve as the anode. The cathode is principally comprised of water. The electrolyte can be solid or liquid. For lithium, the principal reactions are:
______________________________________ Anode Li - e.sup.- .fwdarw. Li.sup.+ Cathode H.sub.2 O + e.sup.- .fwdarw. OH.sup.- + 1/2H.sub.2 Overall Li + H.sub.2 O .fwdarw. LiOH + 1/2H.sub.2 ______________________________________
However, as apparent from the overall electrochemical reaction, lithium and water will also react directly with one another, essentially resulting in parasitic corrosion of the anode when exposed to water. The corrosion reaction is highly undesirable because it produces no useful electrical energy and consumes active lithium. The reaction is highly exothermic and can detrimentally accelerate local corrosion. Further, the produced lithium hydroxide reacts with water and eventually precipitates as a monohydrate crystal. Accordingly, a principal challenge with respect to reactive metal-water batteries is development of techniques that minimize this parasitic corrosion, thereby extending battery life and improving efficiency. With liquid electrolytes, this has typically focused on liquid additives that enhance or result in formation of a calcareous film upon the outer surface of the lithium metal as a means of protecting the metal from contact with water. Work has also been conducted in the past with solid polymer electrolytes, but without much success due to one or both of low current output and water permeability which shortens life.
Accordingly, needs remain for improved reactive metal-water batteries and solid polymer electrolytes therefor. While the invention was principally motivated in solving problems with respect to this particular art area, the artisan will appreciate applicability of the invention in other areas, with the invention only being limited by the accompanying claims appropriately interpreted in accordance with the Doctrine of Equivalents.